For automotive applications, batteries with free electrolyte are still maintaining their pre-eminent position in the industry due primarily to lower cost as well as ease of manufacturing. Furthermore, the flooded battery designs are known to have certain technical advantages in comparison to acid-starved designs; but the major limitation of these (flooded) designs lies in their inherent possibility of acid leakage during handling, transportation and charging, resulting from internal pressure build-up. As a result, a small percentage of automotive batteries are being converted to leak proof, VRLA (Valve Regulated Lead Acid) type assembled with AGM (Absorptive Glass Mat) separators in spite of a substantial cost penalty.
It will be noted from the above that there is a strong need to develop low cost, leak retardant/resistant batteries containing free electrolyte, particularly suitable for the use in the automobiles.
Hitherto, there have been many attempts to develop leak resistant battery with free electrolyte using special design of battery covers. Of the several patents filed in this connection, a few of them are being cited below for reference in view of their relative importance:
Patent No. Publication Date
U.S. Pat. No. 5,843,593 filed Dec. 1, 1998; U.S. Pat. No. 5,683,830 filed Nov. 4, 1997; U.S. Pat. No. 5,424,146 filed Jun. 13, 199; U.S. Pat. No. 5,380,604 filed Jan. 10, 1995; EP 0639862 B1 filed Sep. 18, 1996.
In most of the patents cited above, leak retardant characteristics are achieved by using a relatively complex design battery cover, which usually is composed of an upper lid and a lower lid. More particularly, there is a second part of the battery cover, which is fixed with the main cover either by heat sealing or ultrasonically. In the event of battery tilting sideways or in the inverted position, some electrolyte flows out from the container into the space provided between the two parts of the battery cover, which is then allowed to flow back when the battery is restored to its upright position.
The design based on two-piece battery cover is relatively expensive and more complex at the manufacturing stage. Clearly, there is a need for a simple, one-piece leak retardant cover design without adversely affecting the cost competitiveness.